Any couple who brings personal or business assets to the marriage can benefit from a prenup. The most basic of these contracts lists an inventory of premarital assets that in the event of a divorce will remain the property of their original owner.

"Prenups are good because they preserve the expectations of the parties and prevent surprises in a divorce trial," says attorney Bob Nachshin, a partner in family law firm Nachshin & Langlois LLP in Los Angeles, and co-author of "I Do, You Do ... But Just Sign Here: A Quick and Easy Guide to Cohabitation, Prenuptial and Postnuptial Agreements." "In my 34 years of practice, I've never seen a prenuptial agreement that wasn't enforced by the court."

The agreements can also specify that future income from a business or additional assets accrued through inheritance are not to be shared with your spouse should the marriage end.

"You can basically do anything you want in a prenup, except you can't limit child support, and you can't limit child custody and visitation," says Nachshin.

Yours, mine and oursPrenuptial agreements can address property acquired before a marriage, such as a home or Grandpop's antique desk, although some states recognize each spouse's rights to his or her premarital property anyway, according to attorney Brian Liu, chairman and co-founder of LegalZoom.com, an online law center.

"The problem people have is, after they get married, what's become yours has become co-mingled," Liu says. "People can't trace after 10 years of marriage what was theirs and what's joint property."

Other areas prenups can cover are the waiving of spousal support and death benefits.

"Even if you make a will and exclude your spouse, some courts will look unfavorably on that," Liu says. "If you have a prenuptial agreement, you can say, 'That was my intention to cut out the spouse.'"

Second time aroundPrenups are especially helpful for older couples and/or those who already have children, says Lynne Gold-Bikin, a family law attorney and former chair of the American Bar Association's family law section.

"Older couples may want to protect children from a prior marriage or protect the ability of the one with lesser assets to go into a nursing home and not give everything over," Gold-Bikin says.

People who have been married before are especially aware of the importance of taking these steps the second time around.

"A lot of times, prenuptial agreements have a bad connotation," Liu says. "I see them happening with people who may have been divorced once, and have children and significant assets, and want to make sure their children and family are protected if something happens."

I do's and don'tsStates have different rules for prenups. California requires an agreement be signed at least seven days after it has been presented, that both parties have attorney representation and that all assets should be disclosed, Nachshin says.

Those requirements were added to the law after the state Supreme Court upheld baseball star Barry Bonds' prenuptial agreement, despite it being signed a day before his wedding and without his future wife having counsel, according to Nachshin, who represented Bonds.

Other circumstances to keep in mind are to never sign such an agreement after having a few drinks and to not present such an agreement when a woman is pregnant, because her medical condition could lead to it being overturned, Nachshin says.

"Remember to talk about it with your spouse way before you plan your wedding, and have it signed four months before you plan on getting married," Nachshin says. "Because otherwise, you're so focused on the prenup that you can't focus on the joy of marriage."

Why 'pre' is better than 'post'For couples who didn't enter into a prenuptial agreement, they always have the option of forging such a pact after they say their vows. Postnuptial agreements are largely the same as prenups, laying out which assets will remain individual property and which will be shared.

However, states may view postnups differently if they are challenged during a divorce. In California, for example, prenups are presumed to be legally valid, while postnups are presumed to be invalid — meaning the burden of proof with the latter is on the spouse trying to have the terms enforced, Nachshin says.

"I think if both parties have counsel, and there's been full disclosure, the postnup will be upheld," he says.

What's fair?Prenuptial agreements are supposed to be based on fair and full disclosure of assets, but states vary in how they view this legal tenet, says Gold-Bikin.

The prenup "has to be considered fair at the time it's enforced," she says.

For example, a spouse may agree she won't take anything from a business that's worth $100 at the time she and her future husband sign the prenup. By the time the couple divorces, the husband has transformed the business into the next Google or sold it for a big profit.

Whether it was a "fair agreement" for the wife to not share in the business depends on the state, Gold-Bikin says.

Separate accountsThere are other ways to keep assets separate that can work in conjunction with a prenup, or alone.

A revocable living trust can ensure that certain property or income is directed to someone other than your spouse, Liu says.

An even simpler tool is to retain separate bank accounts and keep real estate under your own names.

"Some people, when they get married, immediately change title to property so it's in both their names," Liu says. "The fact that you put the other spouse on the deed, (a judge) is going to assume you meant to give half of your interest to the spouse as a gift, and is going to consider that joint property."

What can gay couples do?Same-sex couples living in states where their union lacks legal recognition can draw up a co-habitation agreement that resembles a prenup. Similar rules apply: Each partner should have his or her own attorney, disclose assets and not sign the pact under duress, Nachshin says.

With same-sex marriage legal in six states and the District of Columbia, this developing area of the law is made complicated by the fact that a vast majority of states don't allow such unions or recognize their legality.

"As more and more same-sex couples get married, they will experience the same thing as heterosexual couples — they're going to get divorced," Gold-Bikin says. "The next time they get married, they will have prenuptial agreements."

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